This study will evaluate the immunogenicity of pneumococcal conjugate vaccine and the capacity to prime in patients with sickle cell disease, as compared to polysaccharide pneumococcal vaccine. Sickle cell patients are at risk for pneumococcal, meningococcal, and H. Influenzae type b (HIB) infections. Immunizations are recommended for all sickle cell patients with reimmunization of pneumococcal vaccine every 3-5 years for children less than 10 and every 6 years for those older. Pneumococcal vaccine has limited efficiency in young patients and overall only 75% efficacy. Newer pneumococcal-conjugate vaccines have been produced that are more immunogenic and prime for later responses. The randomized study will compare two doses of pneumococcal-conjugate vaccine followed by 23-valent vaccine to one dose of 23-valent vaccine only. All subjects will also receive HIB-conjugate and meningococcal vaccines.